An equation has been derived to compare the costs of two schemes for recycling spent fuel to light-water reactors: diffusion and blending. The calculations show that blending is slightly more costly than diffusion. The factors that can chiefly influence this conclusion are the discharge enrichment and the value of236U. A very high burnup would favor diffusion; a very high price for238Pu and, therefore, for236U, would render blending the desirable route.